Vectorized plot constant (#1524)

Allow constant expression in vectorized Plot3D.

This change affects only the vectorized version; added a test for
constant expression to verify that it works already for Plot3D classic.

Author: bdlucas1

mathics/eval/drawing/plot3d_vectorized.py

@@ -23,21 +23,21 @@ def eval_Plot3D(
 ):
     graphics = GraphicsGenerator(dim=3)
 
-    for function in plot_options.functions:
-        # pull out plot options
-        _, xmin, xmax = plot_options.ranges[0]
-        _, ymin, ymax = plot_options.ranges[1]
-        nx, ny = plot_options.plotpoints
-        names = [strip_context(str(range[0])) for range in plot_options.ranges]
+    # pull out plot options
+    _, xmin, xmax = plot_options.ranges[0]
+    _, ymin, ymax = plot_options.ranges[1]
+    nx, ny = plot_options.plotpoints
+    names = [strip_context(str(range[0])) for range in plot_options.ranges]
+
+    # compute (nx, ny) grids of xs and ys for corresponding vertexes
+    xs = np.linspace(xmin, xmax, nx)
+    ys = np.linspace(ymin, ymax, ny)
+    xs, ys = np.meshgrid(xs, ys)
 
+    for function in plot_options.functions:
         with Timer("compile"):
             function = plot_compile(evaluation, function, names)
 
-        # compute (nx, ny) grids of xs and ys for corresponding vertexes
-        xs = np.linspace(xmin, xmax, nx)
-        ys = np.linspace(ymin, ymax, ny)
-        xs, ys = np.meshgrid(xs, ys)
-
         # compute zs from xs and ys using compiled function
         with Timer("compute zs"):
             zs = function(**{str(names[0]): xs, str(names[1]): ys})
@@ -49,6 +49,10 @@ def eval_Plot3D(
         # assert np.all(np.isreal(zs)), "array contains complex values"
         zs = np.real(zs)
 
+        # if it's a constant, make it a full array
+        if isinstance(zs, (float, int, complex)):
+            zs = np.full(xs.shape, zs)
+
         with Timer("stack"):
             # (nx*ny, 3) array of points, to be indexed by quads
             xyzs = np.stack([xs, ys, zs]).transpose(1, 2, 0).reshape(-1, 3)

test/builtin/drawing/test_plot.py

@@ -66,6 +66,7 @@ def test__listplot():
             "-Graphics3D-",
             None,
         ),
+        ("Plot3D[1, {x,-1,1}, {y,-1,1}]", None, "-Graphics3D-", None),
         (
             "Plot3D[]",
             ("Plot3D called with 0 arguments; 3 arguments are expected.",),